In the context of this disclosure, the term ‘promoter’ or ‘promoter region’ refers to a sequence of DNA, usually upstream (5′) to the coding sequence of a structural gene, which controls the expression of the coding region by providing the recognition for RNA polymerase and/or other factors required for transcription to start at the correct site.
There are generally two types of promoters, inducible and constitutive promoters. An inducible promoter is a promoter that is capable of directly or indirectly activating transcription of one or more DNA sequences or genes in response to an inducer. In the absence of an inducer the DNA sequences or genes will not be transcribed. Typically, the protein factor, which binds specifically to an inducible promoter to activate transcription, is present in an inactivated form, which is then directly or indirectly converted to the active form by the inducer. The inducer can be a chemical agent; a physiological stress caused by environmental conditions, or can be an endogenously generated compound in response to changes in the development of the plant.
Constitutive promoters direct the expression of the DNA sequence (gene), which they control, throughout the various parts of the plants and continuously throughout plant development. However, the term ‘constitutive’ as used herein does not necessarily indicate that a gene is expressed at the same level in all cell types, but that the gene is expressed in a wide range of cell types, although some variation in abundance is often observed.
One of the earliest and most important inventions in the field of plant protein expression is the use of (plant) viral and Agrobacterium-derived promoters that provide a powerful and constitutive expression of heterologous genes in transgenic plants. Several of these promoters have been used very intensively in plant genetic research and are still the promoter of choice for rapid, simple and low-risk expression studies. The most famous are the 35S and 19S promoter from Cauliflower Mosaic Virus (CaMV), which was already found to be practical useful in 1984 (EP 0 131 623), and the promoters which can be found in the T-DNA of Agrobacterium, like the nopaline synthase (nos), mannopine synthase (mas) and octopine synthase (ocs) promoters (EP 0 122 791, EP 0 126 546, EP 0 145 338). A plant-derived promoter with similar characteristics is the ubiquitin promoter (EP 0 342 926).
A special group of the inducible promoters are the tissue- or development-specific promoters. These promoters have the property that they drive expression of the gene that they control predominantly in only one or a small group of tissues or predominantly during one developmental stage of the plant. Of course there also will be tissue-specific promoters that are developmental stage specific.
Promoters, which are predominantly functional in callus tissue, are relatively rare. A valuable application of such callus tissue specific promoters could be in the driving of selectable marker genes. During plant transformation selection of transgenics is predominantly done during tissue culture phase when callus is being formed and the callus differentiates into shoot and/or root tissue. Thus, expression of the selectable marker at this stage is required. Further, when the plants are developing into mature plants and in the mature stage itself, expression of the selectable marker serves no use anymore and it can even be considered as counterproductive. One example of this approach is demonstrated by Firek, S. et al. (1993, Plant Molecular Biology 22(1): 129–142), who used the callus-predominant Asparagus Aopr1-promoter to drive expression of the nptII gene. However, the number of this type of alternative promoters available from literature is limited.
It is therefore an aim of the present invention to provide a new plant-derived callus specific promoter.
It is a further aim of the present invention to provide fragments of DNA comprising the promoter according to the present invention.
It is a further aim of the present invention to provide transgenic plants (or parts and/or seeds thereof) comprising the promoter according to the present invention, including plants (or parts of plants) and seeds derived from said transgenic plants.